GEOLOGY OF GILES COUNTY, VIRGINIA 
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ably filling cavities. The granular ore (which is usually sub- 
ordinate to the fossil type) is made up of aggregates of quartz 
grains like fiaxseed in shape, about which the iron oxide has been 
deposited. In the Clinton epoch, iron was deposited in large 
amounts throughout much of eastern North America. This ore 
was carried in solution as bicarbonate in the presence of carbon 
dioxide. When the excess carbon dioxide was removed, ferric 
hydroxide was either precipitated due to oxidation and hydroly- 
sis, or on account of the iron bacteria, which according to 
Harder^® are always active in its accumulation. 
The Bays Formation (Upper Ordovician) is often ferruginous, 
and Bassler has suggested that at least some of the iron of 
the Clinton is due to the erosion of the Bays, together with the 
solution of its iron content, and its subsequent concentration in 
the Bockwood. In a like manner, much of the Devonian ore may 
be due to the erosion of the Rockwood and the later deposition of 
the iron content in the Giles sandstones and shales. 
The deposit of this type of ore over the entire flat summits of 
Angels Rest and Pearis mountains may sometime be developed. 
There are many thousands of tons of poor grade ore in this de- 
posit which might be mined by steam shovel. The small iron 
content and the lack of any facility to get the ore down off the 
mountain prevents the exploitation of this ore body. 
Many of the Brown ore deposits in the Cambro-Ordovician 
limestones appear to have been formed rather recently, probably 
during Tertiary times. (Tertiary fossils have been found in 
these deposits.)^® These ores are alteration products of iron 
carbonate and pyrite, which in turn originated by replace- 
ment of the limestone. The ore often is found filling fissures 
and concentrated in fracture zones. From the structural posi- 
tion of many of the ore bodies, it seems evident that the deposits 
were made when the country had reached a topographic state 
not vastly different from that existing today. 
The best exposures are at Johnson’s near Chapman’s Ferry, 
and at the mouth of Big Stony Creek. Scattered out-crops of 
this ore are found over the entire county. Usually the strati- 
graphic position of the ore is near the contact of the Shenandoah 
with the Chickamauga. 
Harder, E. C., “Iron-depositing Bacteria and their Geologic Relations,” 
U. S. Geol. Survey Prof. Paper No. 113 (1919). 
Eckel, E. C., U. S. Geol. Survey, Bull. 400, pp. 145. 
